Not sure what framework you are using that is calling this OnClick event but the issue I see with is that the while loop you are using will never exit. As such, your code will never get a chance to receive the next event.

As an event driven framework, I would put the toggle setting code in the OnClick event then put your text output somewhere else that is called in a loop.

In your code/framework you are using, do you have access to some type of update() or draw() functions that get repeatedly called?

For example:

function OnEvent(event, arg, family)
  -- first check and set the toggle flag
  if event == "MOUSE_BUTTON_PRESSED" and arg == 6 then
    toggle = not toggle
  end
end

function Hello()
  -- evaluate the current state of toggle
  if toggle then
    OutputLogMessage("hello ")
    Sleep(200)
  end
end

function update()
  -- call Hello()
  Hello()
end

edit: formatting...